Research On Preparation And Properties Of LiNi_0.5Mn_1.5O₄ High-voltage Cathode Material For Lithium-ion Battery

Recently, higher requirements for the development of lithium ion battery are demanded with the rapid change of modern electronic technology. In order to meet the needs of this development better, it is inevitable to research and develop new-type electrode material with excellent performance. Spinel LiNi_0.5Mn_1.5O₄ cathode material with single high voltage discharge platform, can significantly improve the energy density of lithium ion battery, attracting the researchers’ widespread interest. In this paper, a series of LiNi_0.5Mn_1.5O₄ cathode materials have been successfully prepared by co-precipitation method and sol-gel method respectively. The structure and performance of the materials have been analyzed, and effectively improve the material’s electrochemical properties by ion doping.Firstly, LiNi_0.5Mn_1.5O₄ cathode material with excellent performance by single and composite precipitation have been prepared respectively. After comparing and analyzing the structure and electrochemical performance of the materials, it is found that the sample prepared by Na2CO3 and（NH4）2C2O4 as composite precipitator with the sintering temperature of 750 ℃ for 15 h possess high purity and preferable electrochemical performance. The initial discharge specific capacity of the material at 0.2C rate can be reached to 129.6 mAh?g-1. After 50 cycles, about 85.9% of the capacity has been maintained. It is showed that the composite synergistic effect of the two kinds of precipitation agents is helpful to improve the properties of the materials.Cr³⁺ doped electrode materials have been prepared by sol-gel method with glycine as chelating agent. The electrochemical performance of the materials have been studied. The results show that doping with Cr³⁺ has no effect on the crystal structure and morphology of the materials. When the molar content of Cr³⁺ is 0.05, the electrochemical performance of LiNi0.45Cr0.05Mn1.5O4 cathode material exhibits the best properties, which can reach 113.3mAh·g-1 at 0.2C rate. Comparing with the undoped sample, the capacity retention has been increased 13% after 30 cycles. This should be attributed to the inhibition of electrode polarization by doping with Cr³⁺, which can play an important role on the cycle performance of the material.On the basis of the optimal doping amount of Cr³⁺, the modifying mechanism of co-doping by Cr³⁺ and Co²⁺ has been further researched. Through analysis, we have foundthat when the molar content of Cr³⁺ and Co²⁺ are 0.02 and 0.03 respectively, the material could achieve 126.4 mAh·g-1 at 0.2C rate. Compared with the LiNi0.45Cr0.05Mn1.5O4 cathode material, the discharge specific capacity have been increased 13.1 mAh·g-1. This results show that co-doping by Cr³⁺ and Co²⁺ can significantly improve the discharge specific capacity of the material, but the cycle performance also needs to be improved.